[jmb99]

My house currently is sitting at 35% humidity while being very poorly ventilated (~900ppm CO2). In the summer, it’s around 50% with the same level of ventilation. This generally has been the case everywhere I’ve lived; in the summer, you’re cooling air, which (all else equal) increases the relative humidity of that air. In the winter, you’re heating air, which decreases the relative humidity of that air.

[littlestymaar]

> while being very poorly ventilated (~900ppm CO2)

Aren't you missing a zero of something? Because 900ppm isn't “very poorly ventilated”.

[crazygringo]

It absolutely is poorly ventilated.

I notice I'm not as mentally focused once it gets to 800 or so.

I have a CO2 monitor to keep it below 600 for productivity and concentration.

Remember, fresh air is around 420.

[littlestymaar]

It's “less than ideal” level of ventilation, but it's also very far from “very poorly ventilated” (it's not even above the target level set by workplace regulation in my country, which is 600ppm above the baseline).